Proper packaging of microelectromechanical systems (MEMS) is important to achieve and maintain device performance in target application environments. Microsystem packaging can account for up to 80% of device manufacturing cost and is a factor that has limited the successful commercialization of certain microsystems. Compared to integrated circuit packaging, microsystem packaging can have a higher level of complexity due to the diversity of device types and/or the necessity for such devices to interact with the surrounding environment.
Some microsystem packaging has been adapted from packaging originally developed for integrated circuits. In one example, device chips are released from a wafer, individually attached, wire-bonded, and then encapsulated in standard or customized dual in-line packages, ball grid arrays, etc. Various wafer-level packaging approaches may also be employed. In a typical implementation, the device chips are separated from each other but remain on a carrier wafer. Each chip is then encapsulated at the wafer scale using techniques such as low-temperature solder-based wafer bonding before the packaged chips are diced and ready for use. These techniques can provide adequate protection for microsystems in some environments, and some have been commercialized. However, such packaging is not suitable for use in certain environments (e.g., harsh environments).
Fossil fuel exploration and production is one example of an industry where microsystems, though often desirable for use, have traditionally been unable to withstand the harsh environments present in oil wellbores or hydraulic fractures. Information regarding temperature, pressure, and other variables in such wellbores, hydraulic fractures, and reservoirs is valuable for maintaining quality, efficiency, and safety in the industry. Techniques such as well logging, cross-well imaging, and seismics can provide aggregate information but would be more useful if supplemented by microsystems with data logging capabilities. However, the harsh subterranean environments and size constraints have limited such use of microsystems. To be successfully used in some applications (such as the aforementioned harsh subterranean environments and size constraints), microsystems must withstand high pressures (e.g. 2500-7500 psi) and high temperatures (e.g. 75-125° C.) in high salinity (e.g. 5-15%) or other corrosive fluids. Furthermore, in order for such microsystems to be flushed with proppants into hydraulic fractures and subsequently retrieved, the packaging must be about 1 mm or less at its largest dimension.